Converters and inverters for photovoltaic power systems

ABSTRACT

A power system includes a plurality of DC/DC converters and a DC/AC inverter. The plurality of DC/DC converters having outputs electrically connected in parallel for supplying a DC voltage bus to an input of the DC/AC inverter. The plurality of DC/DC converters each include a maximum power point tracker (MPPT). Various DC/DC converters and DC/AC inverters suitable for use in this system and others are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/388,417 filed on Sep. 30, 2010. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to photovoltaic power systems, DC/DCconverters and DC/AC inverters for use in such systems, and relatedmethods.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Photovoltaic (PV) devices convert sunlight to electricity. A PV devicemay consist of a single panel, multiple panels, rigid panels, flexiblepanels, serial panels, parallel panels, etc. The output of a PV deviceis typically unregulated (i.e. the output varies with changes insunlight intensity, temperature, etc.). Further, the output of one PVdevice may differ from the output of another PV device due tomanufacturing variations, different operating temperatures, unequalageing, different positioning and/or mounting angles, different shadingfrom trees, structures or clouds, different amounts of dirt or debris onthe respective PV devices, etc.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

According to one aspect of the present disclosure, a power systemincludes a plurality of DC/DC converters and a DC/AC inverter. Theplurality of DC/DC converters have outputs electrically connected inparallel for supplying a DC voltage bus to an input of the DC/ACinverter. Further, each DC/DC converter includes a maximum power pointtracker (MPPT).

According to another aspect of the present disclosure, a DC/DC converterincludes an input, an output, at least one power switch coupled betweenthe input and the output, and a controller configured to provide a powerdelivery curve having a power-decreasing-with-voltage region.

According to another aspect of the present disclosure, a DC/DC converterincludes an input, an output, at least one power switch coupled betweenthe input and the output, and a controller having a maximum power pointtracker (MPPT). The controller is configured to run its MPPT when theoutput voltage of the DC/DC converter is pulled below a first voltage.

According to yet another aspect of the present disclosure, a DC/DCconverter includes an input, an output, at least one power switchcoupled between the input and the output, and a high resistance path forlimiting start-up current.

According to still another aspect of the present disclosure, a DC/ACinverter includes an input, an output, and a controller configured tomaintain a voltage at the input within a defined voltage range.

Some example embodiments of power systems, DC/DC converters, DC/ACinverters and related methods incorporating one of more of these aspectsare described below. Additional aspects and areas of applicability willbecome apparent from the description below. It should be understood thatvarious aspects of this disclosure may be implemented individually or incombination with one or more other aspects. It should also be understoodthat the description and specific examples herein are provided forpurposes of illustration only and are not intended to limit the scope ofthe present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a block diagram of a system comprising a plurality of DC/DCconverters for supplying power to a DC/AC inverter according to oneexample embodiment of the present disclosure.

FIG. 2 is a block diagram of the system of FIG. 1 coupled to a pluralityof photovoltaic (PV) panels according to another example embodiment.

FIG. 3 is a general block diagram of a DC/DC converter according toanother example embodiment.

FIG. 4 illustrates example power delivery curves for the converter ofFIG. 3 according to another example embodiment.

FIG. 5 illustrates additional example power delivery curves for theconverter of FIG. 3.

FIG. 6 is a block diagram of an example two-stage embodiment of theDC/DC converter of FIG. 3.

FIG. 7 is a schematic diagram of a DC/DC converter according to anotherexample embodiment of the present disclosure.

FIG. 8 is a block diagram of a system comprising a plurality of DC/DCconverters for supplying a bus voltage to another DC/DC converteraccording to another example embodiment.

FIG. 9 is a block diagram of a system comprising a plurality of DC/DCconverters for supplying a bus voltage to a DC bus according to yetanother example embodiment.

FIG. 10 is a block diagram of a system comprising a plurality of DC/DCconverters for supplying a bus voltage to one or more batteriesaccording to still another example embodiment of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

A system according to one example embodiment of the present disclosureis illustrated in FIG. 1 and indicated generally by reference number100. As shown in FIG. 1, the system 100 includes two DC/DC converters102, 104 and a DC/AC inverter 106. Each DC/DC converter has an input108, 110 for connection to an input power source. The converters alsoinclude outputs 112, 114 electrically connected in parallel to provide aDC voltage bus to an input 116 of the DC/AC inverter. The bus voltagemay be fixed or variable.

Each converter 102, 104 includes a maximum power point tracker (MPPT)that endeavors to harvest maximum power from its input power source.Additionally, each converter 102, 104 is preferably configured tooperate independently of any external control signal (e.g., from asystem controller or another DC/DC converter). The converters 102, 104may be substantially identical to one another. Alternatively, converter102 may be a different type and/or size than converter 104. In someembodiments, each converter is sized to match its input power source.

The inverter 106 may be an isolated or non-isolated inverter.Preferably, the inverter 106 is configured to control the bus voltageprovided to its input 116. For example, the inverter 116 may control theamount of current it draws from the converters to control the busvoltage.

The inverter 106 may also include an MPPT (in addition to the converterMPPTs). If the inverter 106 does not include an MPPT (and even if itdoes), it is preferably configured to regulate its input voltage and/orcurrent in a manner that is compatible with operation of the converterMPPTs (e.g., so the inverter presents a sufficient but not excessiveload to the converters during normal operation). Further, the inverter106 may be a grid-tie inverter (i.e., configured for connecting itsoutput 118 to a utility power grid) or a non-grid-tie inverter (e.g., aresidential inverter).

Although two converters 102, 104 are shown in FIG. 1, it should beunderstood that less (i.e., one) or more converters may be used in otherembodiments of this disclosure. Further, it should be understood thatthe converters 102, 104 may be used in other systems apart from theinverter 106, and the inverter 106 may be used in other systems apartfrom the converters 102, 104, without departing from the scope of thisdisclosure.

The system 100 of FIG. 1 can be used with photovoltaic (PV) input powersources, as shown in FIG. 2. More specifically, the converter inputs108, 110 may be coupled to photovoltaic (PV) panels 202, 204. Panel 202may be a different type and/or size of panel than PV panel 204. In thatevent, the type and size of converters 102, 104 are preferably matchedto the type and size of panels 202, 204, respectively. The flexibilityto mix-and-match converters of various types and/or power ratings allowseach DC/DC converter to be optimized for its input power source.

Each converter may be physically mounted behind or near its associatedPV panel. Alternatively, one or more converters may be located away fromits panel, e.g., in a central area, etc.

Preferably, the MPPT in each converter 102, 104 adjusts its inputvoltage and/or input current as necessary to track the maximum powerpoint (MPP) of its PV panel 202, 204 and thereby extract maximum powerfrom the panels. As noted above, the inverter 106 may also include anMPPT for maintaining the bus voltage and/or bus current at level(s) thatmaximize the amount of overall power extracted from the panels andconverters as a group. For example, the inverter 106 may be anoff-the-shelf grid-tie solar inverter having an MPPT.

If the inverter 106 does not include a MPPT (and even if it does), theinverter is preferably configured to maintain its input voltage and/orinput current at level(s) that do not interfere with operation of theconverter MPPTs. For example, if each converter 102, 104 is configuredto run its MPPT when the converter's output voltage is between 300 and400 VDC, the inverter 106 may be configured to maintain its inputvoltage (i.e., the bus voltage) between 300 and 400 VDC. In this manner,the inverter 106 can maximize the amount of power harvested from the PVpanels 202, 204 by the converters 102, 104.

Although only two converters 102, 104 and two PV panels 202, 204 areshown in FIG. 2, it should be understood that more converters and PVpanels can be used in other embodiments. Further, while each converter102, 104 is coupled to the output terminals of only one PV panel in theexample of FIG. 2, each converter may be coupled to series or parallelcombination(s) of multiple PV panels in other embodiments of thisdisclosure.

FIG. 3 illustrates a DC/DC converter 300 suitable for use as one of theconverters 102, 104 in FIGS. 1 and 2. As shown in FIG. 3, the DC/DCconverter 300 includes an input 302, an output 304, a controller 306,passive components 308, and active components 310. The controller 306 ispreferably a digital controller. The controller 306 is configured tooperate one or more of the active components 310 (e.g. power switches,etc.) to control operation of the converter 300. The controller 306 isalso configured to perform a MPPT method for tracking the maximum powerpoint of an input power source coupled to the input 302. For example,the controller 306 may be configured to adjust the duty cycle of one ormore power switches as necessary to draw substantially maximum powerfrom the input power source. Suitable MPPT methods includeperturb-and-observe (“P & O”), constant input current regulation,constant input voltage regulation, predictive maximum power pointtracking using defined characteristics of the input power source, etc).

In addition, the controller 306 need not be responsive to any externalcontrol signals (i.e., the controller may be configured to controloperation of the converter 300 independently). In the example embodimentof FIG. 3, the controller 306 is not responsive to any external controlsignals (e.g., from a central controller or another DC/DC converter).

The converter 300 may include one or more power stages. Each stage mayemploy any suitable power conversion topology including buck, boost,buck-boost, etc. Additionally, one or more stages may be galvanicallyisolated (e.g., via an isolation transformer). The converter's MPPT maybe implemented via the first and/or subsequent stages (when applicable)of the converter.

Additionally (or alternatively), the controller 306 may be configured(e.g., via software) to run its MPPT when the output voltage of theconverter is pulled below a threshold level (e.g., by the load). Forexample, the controller may initially run an output voltage (or current)regulation mode. Subsequently, when the output voltage is pulled belowthe voltage regulation level (e.g., indicating the presence of a load),the controller may switch from the voltage regulation mode to an MPPTmode.

In addition (or alternatively), the controller 306 may be configured tostop running its MPPT when, e.g., the output voltage returns (i.e.,rises) to the voltage regulation level. In that event, the controller306 may revert to the voltage regulation mode. In this manner, if a load(e.g., the inverter 106) stops accepting maximum power from theconverter, the converter may stop supplying maximum power.

In addition (or alternatively), the controller 306 may be configured tostop running the MPPT when the output voltage (or current) reaches athreshold level, such as a low voltage threshold. During the MPPT mode,the output current generally increases as the output voltage decreases.The controller will preferably stop running the MPPT when the outputvoltage of the converter (or another converter voltage) falls below adefined voltage to prevent high current damage to the converter. At thesame time, the controller may shutdown completely, disable one or morestages of the converter, revert to a voltage or current regulation mode,etc. In the event multiple converters of the type shown in FIG. 3 areused in the system 100, the threshold levels (e.g., voltage thresholds)at which each converter starts and/or stops its MPPT may be the same.Alternatively, the threshold level(s) for one converter may be differentthan the threshold level(s) of one or more other converters. Forexample, the voltage threshold levels of multiple converters may bestaggered with respect to one another, so the converters start and/orstop delivering maximum power to the load in a defined sequence (e.g.,one at a time, two at a time, etc.). Thus, one converter may startdelivering maximum power when the bus voltage is pulled below 400 VDC,another converter may start delivering maximum power when the busvoltage is pulled below 398 VDC, and so on.

Additionally (or alternatively), the controller 306 may be configured toprovide a power-decreasing-with-voltage region. For example, theconverter may have one of the power delivery curves 400 shown in FIG. 4.The example power delivery curves 400 include apower-decreasing-with-voltage region 402. In this region 402, the outputpower of the converter decreases as the output voltage decreases below300 VDC. The example curves 400 (for various input power levels) alsoinclude a constant power region 404. In this region 404, the converteris running its MPPT so the output voltage of the converter increases asthe output current decreases (and vice versa), assuming the power inputto the converter is substantially constant. The transition betweenregions 402 and 404 is referred to as the knee voltage 406.

The power-decreasing-with-voltage region 402 is particularly useful whenthe converter is coupled to an inverter having a MPPT. Because pullingthe converter output voltage below 300 VDC will reduce rather thanmaximize the power input to the inverter, the inverter's MPPT willgenerally maintain the converter output voltage (e.g., the bus voltagein FIGS. 1 and 2) above the knee voltage 406 (i.e., above 300 VDC in theexample of FIG. 4).

In the example power delivery curves 400 of FIG. 4, the output power ofthe converter decreases linearly as the output voltage decreases belowthe knee voltage 406. Alternatively, the output power may decreasenon-linearly. For example, the converter 300 may have one of the powerdelivery curves 500 shown in FIG. 5. The example power delivery curves500 include a first power-decreasing-with-voltage region 502 and asecond power-decreasing-with-voltage region 503, as well as a constantpower region 504. The second region 503 has a greater slope than thefirst region 502. As a result, the power delivery curves 500 have agentler transition from the constant power region 504 to the firstpower-decreasing-with-voltage region 502 (at the knee voltage 506) thanfrom the first power-decreasing-with-voltage region 502 to the secondpower-decreasing-with-voltage region 503.

Although the example power delivery curves of FIGS. 4 and 5 havepower-decreasing-with-voltage regions that extend between zero and 300VDC, it should be understood that other voltage ranges (including thosethat begin well above zero volts) and other power delivery curves may beemployed in other embodiments of this disclosure.

When the input of the converter 300 is coupled to a PV panel (such as PVpanel 202 or 204), the power delivery curve(s) of the converter arepreferably similar to the power delivery curve(s) of its PV panel. As aresult, the converter will respond to the inverter (which may be a solarinverter designed for coupling directly to a PV panel) like a PV panel.

Additionally (or alternatively), the converter 300 may include a highcurrent path to limit current flow under certain conditions, such asduring start-up of the converter. For example, the converter 300 mayinclude two power stages as shown in FIG. 6. In particular, theconverter 300 may include a first power stage 602 coupled to a secondpower stage 604 by a resistor 606. A switch 608 may be connected inparallel with the resistor for selectively bypassing (i.e., electricallyshorting) the resistor 606. When the switch is open, the resistor limitsthe amount of current delivered to the second stage. When the switch isclosed, the resistor is effectively removed and no longer limits theflow of current between the first and second stages. In someembodiments, the switch 608 is held open during start-up of the secondstage 604. During this time, the resistor 606 provides a high resistancepath that limits current. Subsequently, when the output voltage (oranother voltage) of the converter reaches a defined level, the switch608 may be closed to bypass the resistor and allow increased currentflow to the second stage (and the load). Similarly, when the outputvoltage of the converter falls below a defined level (e.g., indicatingthe load is pulling too much current), the switch 608 may be opened tolimit current flow. Further, the converter 300 may be configured to openthe switch when the output voltage of the first stage 602 cannot bemaintained above the input voltage of the first stage 602 (particularlyif the first stage 602 employs a boost topology).

Additionally, the example circuit configuration of FIG. 6 protects theconverter 300 from short circuit faults at its output (e.g., on thevoltage bus of FIGS. 1 and 2), as well as from damage that couldotherwise result if the converter 300 is connected (e.g., in system 100)with the wrong polarity.

In addition (or alternatively), the converter 300 may be configured tolimit start-up current in other ways, to protect the converter and/or toprevent exceeding the current capacity of its input power source. As anexample, the controller 306 may be configured to constrain the dutycycle of a power switch until the output voltage (or another parameter)of the converter reaches a threshold level.

Alternatively (or additionally), the converter 300 may include one ormore diodes for preventing reverse current flow to a power sourcecoupled to the input (such as PV panels 202, 204).

FIG. 7 illustrates another example DC/DC converter 700 suitable for useas one of the converters 102, 104 in FIGS. 1 and 2. As shown in FIG. 7,the DC/DC converter 700 includes an input 702, an output 704, and aswitching power supply 706 coupled between the input 702 and the output704. The switching power supply 706 is a two-stage boost converter thatincludes a first stage 708, a second stage 710, a controller 712, aswitch Q2, and a resistor R2. The switch Q2 couples the first stage 708to the second stage 710. The resistor R2 is connected in parallel withthe switch Q2. The second stage 710 includes an isolation transformerTX1 and a diode bridge 714.

In the example of FIG. 7, the second stage 710 is an isolation busconverter stage that steps up the output voltage of the first stage 708with galvanic isolation to a desired second voltage level. Morespecifically, the second stage 710 is a fixed frequency resonant halfbridge converter configured for operating near boundary conduction mode.Zero voltage and zero current switching are also employed for highefficiency.

Additionally, the converter 700 of FIG. 7 may include one or more (e.g.,all) of the features of converter 300 described above with reference toFIGS. 3-6.

An example operation of the converter 700 will now be described withreference to FIGS. 2 and 7. For this example, assume the converters 102,104 in FIG. 2 each have the circuit configuration shown in FIG. 7. Inother words, assume two identical converters 700 are used as theconverters 102, 104 in FIG. 2. The following description will focus onconverter 102 and PV panel 202, but may also apply to converter 104 andPV panel 204.

Preferably, the first stage 708 of converter 102 is configured to boostits input voltage to a level greater than the maximum open circuitvoltage expected from its PV panel 202. Assuming the maximum opencircuit voltage of panel 202 is 75V, the output voltage of the firststage 708 may be 80V. Assuming further the desired output voltage of thesecond stage 710 is 400 V, the second stage requires a 1:5 boost ratio.

When energy is available from the PV panel 202 and the panel voltage isgreater than a minimum threshold level, an internal auxiliary powerconverter (not shown in FIG. 7) will start up to generate internal biasvoltages for the converter 102. If the PV panel 202 does not producesufficient power to start the low power auxiliary converter for biasing,the auxiliary converter will continue its attempts to turn on. When thepanel 202 produces sufficient energy to start the auxiliary converter(to power the controller 712), the controller 712 will attempt to startthe first stage 708. If the panel 202 does not produce sufficient powerto sustain the minimum no load power of the first stage 708, repeatedattempts may be made. This behavior is expected at dawn, when radiationincreases with the rising sun. At some point, the first stage 708 willstart up and deliver a regulated output voltage of 80V at no load.During this time, switch Q2 is disabled (i.e., open) and the secondstage 710 is disabled.

Once the first stage 708 is successfully started, the second stage isenabled. Initially, switch Q2 is held off (i.e., open) so the secondstage 710 receives only limited power due to the resistor R2. Duringthis time, a PV input voltage regulation loop may be activated to ensurethe voltage provided by the panel 202 does not slip to zero. Theregulated input voltage level may be, for example, 70% of the inputvoltage observed before the second stage 710 was enabled. The 70% levelmay be used if the MPP voltage of panel 202 is between 75% to 85% of itsopen circuit voltage. Alternatively, another input voltage regulationlevel may be employed.

The inverter 106 may include a large bulk capacitance that will create anear short-circuit on the output 704 of the converter 102 during thepower-up cycle. Also, other DC/DC converters connected in parallel withconverter 102 (including converter 104) may not start at the same time.Due to the series insertion of R2, the output voltage of the secondstage 710 will rise slowly, allowing the controller 712 to identify thenature of the load. The voltage at the output 704 is reflected acrosscapacitor C3 where it may be monitored by the controller 712. As thisvoltage rises and exceeds the 70% clamp level set for controlling theinput voltage, the switch Q2 is turned on. Now more energy can besupplied to charge the load capacitance as the current limit resistor R2has been bypassed.

As the converter 102 starts to deliver power to the inverter 106, thecontroller's MPPT is activated to monitor the PV input current andvoltage and operate as close to the MPP as possible.

The current limit network of switch Q2 and resistor R2 also protects theconverter 700 from short circuit faults on the output 704 and mayprevent damage if the converter 700 is connected with wrong polarity.The current limit network may prevent the destruction of the converterconnected in wrong polarity as other parallel converters will see ashort circuit and may operate in current limit mode. Each converter mayeventually disable itself if the control circuit observes that theoutput bus voltage is not able to rise in preset time duration.

In this example embodiment, the second stage 710 includes an isolationtransformer TX1 which galvanically isolates the input 702 from theoutput 704. Further, the second stage 710 includes a diode bridge 714which prevents current from flowing from the output 704 to the input702.

It should be understood that, in other embodiments of this disclosure,the inverter 106 in FIGS. 1 and 2 can be omitted and/or replaced byanother component. For example, the inverter 106 can be replaced by aDC/DC converter (as shown in FIG. 8), e.g., for reducing or increasingthe DC bus voltage level. Alternatively, the inverter 106 may be omittedso the DC bus voltage provided by the converters 102, 104 may be coupledto a DC bus (e.g., a 48V or 400V bus in a DC power distribution system),as shown in FIG. 9. In that event, the converters 102, 104 (and possiblyadditional converters all connected in parallel) may be either the soleor a supplemental power source for the DC bus. As another alternative,the inverter 106 may be omitted so the DC bus voltage provided by theconverters 102, 104 may be coupled to one or more batteries (including abattery bank), as shown in FIG. 10. In that event, the DC bus voltageprovided by the converters 102, 104 is preferably slightly greater thanany grid fed battery charger so, e.g., power is drawn from the PV panels202, 204 first, and then from the utility grid.

The devices and methods of the present disclosure are not limited tophotovoltaic applications. For example, the devices and methods of thepresent disclosure may be used with other distributed powerapplications.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1-4. (canceled)
 5. A DC/DC converter having an input, an output, atleast one power switch coupled between the input and the output, and acontroller having a maximum power point tracker (MPPT), the controllerconfigured to run its MPPT when the output voltage of the DC/DCconverter is pulled below a first voltage.
 6. The DC/DC converter ofclaim 5 wherein the controller is configured to regulate its outputvoltage until the output voltage is pulled below the first voltage. 7.The DC/DC converter of claim 5 wherein the controller is configured tostop running its MPPT when the output voltage rises to the firstvoltage.
 8. The DC/DC converter of claim 5 wherein the controller isconfigured to stop running its MPPT when the output voltage reaches asecond voltage lower than the first voltage. 9-17. (canceled)